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Procedia Engineering 00 (2017) 000–000 Procedia Engineering 00 (2017) 000–000 www.elsevier.com/locate/procedia ScienceDirect www.elsevier.com/locate/procedia Procedia Engineering 202 (2017) 159–167

4th International Colloquium "Transformer Research and Asset Management” 4th International Colloquium "Transformer Research and Asset Management” response and harmonic testing of inductive voltage transformer used for power quality measurements Dalibor Filipović-Grčića, Božidar Filipović-Grčićb*, Danijel Krajtnerc Dalibor Filipović-Grčića, Božidar Filipović-Grčićb*, Danijel Krajtnerc aKončar – Electrical Engineering Institute, Fallerovo šetalište 22, 10000 Zagreb, Croatia a b*UniversityKon ofčar Zagreb, – Electrical Faculty Engineering of Electrical Institute, Engineering Fallerovo and Computing,šetalište 22, Unska10000 3,Zagreb, 10000 Croatia Zagreb, Croatia b *UniversitycKon of čZagreb,ar – Instrument Faculty Transformersof Electrical Engi Inc.,neering Josipa andMokrovi Computing,ća 10, 10000 Unska Zagreb, 3, 10000 Croatia Zagreb, Croatia cKončar – Instrument Transformers Inc., Josipa Mokrovića 10, 10000 Zagreb, Croatia

Abstract Abstract International standards related to power quality measurements define methods and accuracies for the measuring instruments, but do not specify Internationalthe accuracy standardsof instrument related transformers. to power qu Therefore,ality measurements it is not possible define meto thodsspecify and an accuracies overall accuracy for the formeasuring such measurements. instruments, butInductive do not voltagespecify transformersthe accuracy of(IVTs) instrument which transformers.are used for Therefore,power quality it is measuremennot possiblets to should specify be an tested overall to accuracydetermine for the such ratio measurements. correction factors Inductive (RCFs) voltage and transformersphase angle errors (IVTs) at whichhigher .are used for Inpower this paper,quality harmonic measuremen distortionts should and frebe quencytested toresponse determine tests the are ratio performed correction to dete factorsrmine (RtheCFs) level and of phaseharmonics angle generated errors at higherby IVT frequencies. and its ability In this to paper, transform harmonic harmonics distortion from and high fre quencyvoltage response (HV) to testslow arevoltage performed (LV) toside. dete Complexrmine the volt levelages of harmonicsconsisting ofgenerated fundamental by IVT voltage and andits abilitycertain toamount transform of superimposed harmonics from harm highonic voltageare used (HV) to check to low the frequencyvoltage (LV) response side. Complexof IVT. RCFs voltages and consistingphase angle of errorsfundamental of the IVTvoltage are and determined certain amount and can of be superimposed applied to power harmonic quality are usedmonitors to check for compensationthe frequency ofresponse errors thatof IVT. occur RCFs at high and phaseharmonic angle frequencies. errors of theDifferent IVT are test determined circuits are andproposed can be for applied generation to power of HV quality consisting monitors of fundamental for compensation voltage ofand errors harmonic that occurvoltages at highwith amplitudesharmonic frequencies. Different test circuits are proposed for generation inof HV consisting of fundamental voltage and harmonic voltagesrange with 5-15amplitudes % of the applied fundamental voltage. In order to improve thein testing capabilities at higher voltage levels (for equipment range with 5-15 % of the applied fundamental voltage. In order to improve the testing capabilities at higher voltage levels (for equipment with 123 kV≤Um≤420 kV), a compensation for both fundamental and harmonic voltages is proposed with a special connection through blocking and pass123 kVfilters.≤Um ≤ 420 kV), a compensation for both fundamental and harmonic voltages is proposed with a special connection through blocking and ©pass 2017 filters. The Authors. Published by Elsevier Ltd. ©Peer-review 2017 The The Authors.under Authors. responsibility Published Published by of Elsevierbythe Elsevierorganizing Ltd. Ltd. committee of ICTRAM 2017. Peer-review under under responsibility responsibility of th ofe organizingthe organizing committee committee of ICTRAM of ICTRAM 2017. 2017. Keywords: Inductive voltage transformer; frequency response; harmonic distortion; power quality; high voltage testing. Keywords: Inductive voltage transformer; frequency response; harmonic distortion; power quality; high voltage testing.

1. Introduction 1. Introduction Voltage harmonic distortion level is one of the significant parameters of power quality in the power system. Higher harmonics causeVoltage the following harmonic effects distortion in electrical level is onenetworks: of the significantadditional parameheatingters and of losses power on quality power insystem the power elements system. (such Higher as transmissio harmonicsn lines,cause thetransformers, following effectscompensation in electrical devices, networks: etc.), additionalunwanted hvoltageeating anddistortion, losses onincreased power system flow ofelements circulating (such currents as transmissio throughn groundinglines, transformers, wire, decrease compensation of transformer devices, rated etc.), power unwanted and inte voltagerference distortion, with conventional increased flowtelecommunication of circulating currentslines. Numerous through problemsgrounding related wire, decreaseto voltage of and transformer current harmonic rated power effects and in intepowerrference systems with are conventional commonly observedtelecommunication nowadays duelines. to Numerousgrowth of largeproblems industrial related consumers to voltage with and currentnon-linear harmonic loads and effects power in powerelectronic systems equipment are commonly [1]. Voltage observed harmonics nowadays may duedisturb to growth sensitive of loadslarge industrialconnected consumers to the grid withand thereforenon-linear they loads should and powerbe limited. electronic Levels equipment and spectral [1]. content Voltage of harmonics voltage may disturb injected sensitive into loadselectric connected grids are to tending the grid to andincrease therefore even they though should the beacceptable limited. levelsLevels are and determin spectraled content by numerous of voltage regulations. distortions IEC injected standards into electric grids are tending to increase even though the acceptable levels are determined by numerous regulations. IEC standards

* Corresponding author. Tel.: +38516129714; fax: +38516129890. * CorrespondingE-mail address: author. [email protected] Tel.: +38516129714; fax: +38516129890. E-mail address: [email protected] 1877-7058 © 2017 The Authors. Published by Elsevier Ltd. Peer-review1877-7058 © under 2017 responsibilityThe Authors. ofPublished the organizing by Elsevier committee Ltd. of ICTRAM 2017. Peer-review under responsibility of the organizing committee of ICTRAM 2017. 1877-7058 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the organizing committee of ICTRAM 2017. 10.1016/j.proeng.2017.09.703

10.1016/j.proeng.2017.09.703 1877-7058 160 Božidar Filipović-Grčić et al. / Procedia Engineering 202 (2017) 159–167 2 Dalibor Filipović-Grčić et al. / Procedia Engineering 00 (2017) 000–000

[2]-[4] define compatibility levels or planning levels for voltage harmonics in LV, MV and HV networks. Furthermore, European standard [5] defines, describes and specifies the main characteristics of the voltage at a network user's supply terminals in public LV, MV and HV networks under normal operating conditions. According to [6], power quality and voltage distortion measurements are carried out by high accuracy measuring equipment of class A. In MV and HV grids this measuring equipment is commonly connected to secondary side of IVTs installed within the substations. So, an overall accuracy of the measurement depends on the accuracy of IVTs. The accuracy requirements in [6] are defined only for the measuring equipment but not for IVTs. The standard for IVTs [7] defines the accuracy limits at rated frequency, but it doesn’t define the accuracy limits at higher frequencies. The accuracy of IVTs for frequencies higher than the nominal frequency is usually not known. It is therefore difficult to specify an overall accuracy not only for harmonic voltage measurements but also for measurement of any kind of transient containing a wide harmonic spectrum. Literature survey [8]-[17] showed that conventional IVTs may have significant difference between the accuracy at rated frequency and the accuracies at higher frequencies. Therefore, a frequency response of IVTs in the concerned range of frequency should be known to use them for harmonic measurements in power system. Different measuring setups and calculation procedures for frequency response of IVTs are presented in [18]-[21]. Significant differences between IVT ratio at rated frequency and at higher frequencies can be observed, caused by resonances within the IVT. Also, a little research has been conducted concerning the angle characteristics of IVTs operating with non-sinusoidal waveforms. To determine the behaviour of the IVT’s ratio and phase angle at higher frequencies two separate tests should be performed: frequency response test and harmonic distortion test. Although different circuit setups for testing the harmonic responses of IVTs are described in literature, only a few of them could achieve the voltage level above 200 kV. Besides, the equipment used in the test circuit setups and test methods are also largely unspecified and differ from each other. In [22], a test circuit is proposed for determining the harmonic responses of IVTs. The frequency response assessment of a single phase 400 kV IVT and a single phase 275 kV capacitor voltage transformer in a range of frequency from 50 Hz up to 5 kHz is presented. However, at 400 kV level the test circuit has a limitation regarding the harmonic injection ability. The maximum of generated voltage harmonics are 1 % with respect to the of the fundamental voltage up to 1 kHz, while the harmonic amplitudes from 1 kHz up to 5 k Hz are lower than 0.2 %. The harmonic injection ability of the test circuit is limited by maximum power capacity of the which was used as a harmonic power source. In this paper, three different test circuits are proposed for generation of HV which consists of fundamental voltage and harmonic voltages with amplitudes in range 5-15 % of the applied fundamental voltage. This is of great importance since high signal to noise ratios reduce measurement uncertainty. The selection of appropriate test circuit depends on highest voltage Um for equipment under test and its required active and reactive power. In order to improve the testing capabilities at voltage levels 123 kV≤Um≤420 kV, a compensation for both fundamental and harmonic voltages is proposed with a special connection through blocking and pass filters. A test method is presented for frequency response and harmonic distortion testing of IVTs used for power quality measurements. Experimental verification is demonstrated in case of medium voltage IVT. RCFs and phase angle errors of the IVT are determined at fundamental frequency and at each harmonic frequency from 2nd to 50th harmonic. These correction factors can be applied to power quality monitors connected to the secondary terminals of the IVT.

2. Test circuits for generation of high voltages containing higher harmonics

2.1. Test circuit with a single source and without compensation

The first test setup shown in Fig. 1 is in most cases suitable for testing of medium voltage equipment. In this test circuit, both fundamental and harmonic voltages are generated from the same source which consists of arbitrary waveform generator (AWG), low frequency amplifier and test transformer. In this case a single source is generating both active and reactive power required by test object and capacitor voltage divider which is used as a reference measuring system.

Fig. 1. Test circuit with single source without compensation.